1. Field of the Invention
The present invention relates to a cyan toner for developing an electrostatic image through a method for forming an image, such as electrophotography and electrostatic printing, a cyan toner for forming toner images through a method for forming an image of a toner jet process, a method for forming an image employing the cyan toner, and a method for forming a full-color image employing the cyan toner. More specifically, the present invention relates to a cyan toner employed in a fixing process in which those toner images are heat-pressure-fixed onto a transfer material such as a print sheet, a method for forming an image employing the cyan toner, and a method for forming a full-color image employing the cyan toner.
2. Description of the Related Art
As an apparatus for forming a color image of an electrophotographic process spreads widely, its application has also prevailed in wide variety, leading to a severe demand on image quality. An extremely fine and faithful reproduction of even fine portions is demanded for a copy or a print of an image, such as general photographs, catalogs, and maps. Along with this demand, a demand toward vividness of color has increased, and an extension of color reproduction range is desired. In particular, a high level of colorfulness, fineness, graininess, etc. equal to or higher than a print quality is demanded for the electrophotographic process as well.
In a recent apparatus for forming an image of an electrophotographic process employing digital image signals, dots of a constant potential form a latent image on a surface of an electrostatic charge image bearing member (for example, photoconductor), and solid portions, halftone portions, and line portions are expressed by changing a dot density. However, a problem tends to occur in that gradation of a toner image corresponding to a ratio of the dot densities of black portions and white portions of the digital latent image cannot be obtained when toner particles fall out of the dot in this method. Further, when enhancing resolution by reducing a dot size to improve the image quality, reproducibility of the latent image formed with minute dots tends to degrade. In addition, the resolution and the gradation of a highlight portion, in particular, degrade, likely resulting in an image lacking in sharpness. Further, irregular dot disarrangement is perceived as graininess and becomes a cause of degrading the image quality of the highlight portion.
A method for forming an image, employing a deep color toner (deep toner) for the solid portion and a toner with lower density (pale toner) for the highlight portion, is proposed for improving the above. JP 11-84764 A and JP 2000-305339 A each disclose methods for forming an image employing a plurality of toners with different densities combined.
Further, JP 2000-347476 A discloses an apparatus for forming an image combining a pale toner having the maximum reflection density of half or less of the maximum reflection density of a deep toner. JP 2000-231279 A discloses an apparatus for forming an image combining a deep toner having an image density of 1.0 or more and a pale toner having an image density below 1.0, when a toner amount of 0.5 mg/cm2 on a transfer material.
Further, JP 2001-290319 A discloses an apparatus for forming an image combining toners with a slope ratio of recording densities of a deep toner and a pale toner between 0.2 and 0.5.
According to studies of the inventors of the present invention, the gradation and the graininess of an image formed applying those conventional technologies may be improved in a low-density region constituting of the pale toner alone. However, an improvement is needed for the graininess in a medium-density region where the deep toner and the pale toner are mixed, and an extension of a color reproduction range is preferred.
For the pale toner, not much was known about an optimum design of hue and density of a colorant for the pale toner and an effect of a kind and an amount of a wax on improvement of the graininess (roughness) of an image in the low-density region and on expansion of a fixing temperature region.